Physics Formula Sheet: What to Memorise vs What to Derive for Classes 11-12

Physics paper-setters at the CBSE, ICSE, state board, and testing agencies like the NTA for JEE and NEET do not reward rote memorisation of three hundred random expressions. If you try to memorise every sub-formula in standard textbooks for the 2026-27 academic session, your working memory will overload by November.

To clear competitive cutoffs and score above $90\%$ in board exams, you must divide your formula sheet into two distinct categories: Direct-Recall Formulas and Derivable Core Identities.

Why Blind Memorisation Fails in JEE and NEET

Consider a standard electrostatics problem. If you memorise fifteen different shortcut formulas for the electric field due to variations of charged rings, disks, and shells, you will likely mix up the powers of $R$ and $x$ under square roots during an actual exam.

However, if you memorise the fundamental definition of Coulomb's Law and Gauss's Law, and know how to apply integration quickly, you can reconstruct any missing expression in under thirty seconds.

For board exams, examiners explicitly award step marks for derivations. Writing a direct final formula without showing the intermediate steps can cost you marks, even if your final numerical answer is correct.

Category 1: Formulas to Memorise (Direct-Recall)

These are fundamental constants, definitions that cannot be simplified further, and standard mathematical shortcuts that save critical seconds during high-pressure timed tests.

Mechanics & Kinematics

Equations of motion under constant acceleration: $v = u + at, \quad s = ut + \frac{1}{2}at^2, \quad v^2 = u^2 + 2as$
Centripetal acceleration and force: $a_c = \frac{v^2}{r} = \omega^2 r$
Moment of inertia for standard symmetric bodies (Ring, Disk, Solid Cylinder, Hollow Cylinder, Solid Sphere, Hollow Sphere, Rod).

Electrodynamics & Magnetism

Coulomb's Law and Electric Field definition: $F = \frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r^2}, \quad \vec{E} = \frac{\vec{F}}{q_0}$
Magnetic force on a moving charge and a current-carrying wire: $F = q(\vec{v} \times \vec{B}), \quad F = I(\vec{L} \times \vec{B})$
Reactance and impedance in an LCR alternating current circuit: $X_L = \omega L, \quad X_C = \frac{1}{\omega C}, \quad Z = \sqrt{R^2 + (X_L - X_C)^2}$

Optics & Modern Physics

Lens Maker's Formula and Thin Lens Formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right), \quad \frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
Einstein's Photoelectric Equation: $K_{\max} = h\nu - \Phi_0$
Radioactive decay law: $N(t) = N_0 e^{-\lambda t}, \quad T_{1/2} = \frac{\ln 2}{\lambda}$

Category 2: Formulas to Derive (On-the-Spot)

Do not waste precious brain space memorising complex multi-variable equations. Instead, practise deriving them weekly until the flow becomes second nature.

| Topic | Complex Expression to Derive | Starting Point / Fundamental Law | | :--- | :--- | :--- | | Gravitation | Potential energy and orbital velocity of a satellite | Newton's Law of Gravitation & Centripetal force balance | | Current Electricity | Drift velocity expression: $I = nAv_d$ | Definition of current, electron density, and relaxation time | | Wave Optics | Fringe width in Young's Double Slit Experiment: $\beta = \frac{\lambda D}{d}$ | Path difference approximation using geometry | | Thermodynamics | Work done in an isothermal process: $W = nRT \ln\left(\frac{V_2}{V_1}\right)$ | Integration of $P \, dV$ using ideal gas law $P = \frac{nRT}{V}$ |

How to Build Your Personal Formula Sheet

When preparing for your Class 11-12 terminal evaluations, board exams, or engineering/medical entrances, follow these rules to maintain your formula repository:

Keep it handwritten: Never print out a generic coaching institute formula booklet and paste it on your wall. The act of writing reinforces memory pathways in your cerebral cortex.
Include validity conditions: Next to every formula, write its constraints. For example, write $\theta$ in radians for fringe width, or note that Bernoulli’s equation requires an incompressible, non-viscous, steady fluid flow.
Dimensional check: Whenever you add a new formula, check its dimensions on both sides. If the dimensions do not match, discard it and check your textbook derivation.

Quick Checklist for Formula Revision

[ ] Memorised basic constants ( $\varepsilon_0, \mu_0, G, h, c$ ) and their units.
[ ] Practised all core derivations from NCERT physics textbooks without looking at solved examples.
[ ] Listed vector vs scalar properties explicitly for fields, forces, and moments.
[ ] Tested formula recall under timed conditions using chapter-wise mock tests on Edumath.